A spun bond non-woven fabric as a typical example of a filament non-woven fabric is produced by a method wherein a group of filaments discharged from a spinneret for melt spinning are drawn and stretched by introducing into an air sucker etc., opened, and accumulated on a collecting conveyor to be formed into a filament web; and then the filaments are entangled or thermally adhered by appropriate means. Therefore, since this non-woven fabric comprises filaments, namely, continuous fibers, it is more excellent in the mechanical properties such as tensile strength etc. as compared with a staple fiber non-woven fabric comprising short fibers. Moreover, since this non-woven fabric is produced by opening and accumulating the filaments obtained directly by melt spinning, it can be rationally produced as compared with non-woven fabrics obtained by opening and accumulating staple fibers by a dry method or a wet method. In recent years, the production of such non-woven fabrics has radically increased.
In particular, a non-woven fabric that comprises conjugated filaments comprising a low melting point resin or a low softening point resin comprising olefin binary copolymer or terpolymer as one component and a crystalline thermoplastic resin as another component is not only advantageous as a filament non-woven fabric from the above mentioned viewpoint, but also is excellent in thermal adhesion, and thus it is easily processable. In a case where the non-woven fabric having excellent properties can be produced, the demand for such non-woven fabric is expected to radically increase.
Moreover, conventionally, absorbent articles such as disposable diapers like paper diapers, sanitary napkins and the like have structures so that body fluids such as urine, blood or the like are absorbed and leakage is prevented. Although the specific structure of such absorbent articles varies between respective embodiments, however, such an absorbent article comprises at least an absorptive core layer for absorbing and retaining body fluids such as urine, blood or the like; a liquid permeable top sheet produced from, for example, a non-woven fabric and located at the side of the front surface of the core layer (the side contacting with the user's skin); and a liquid impermeable back sheet located at the back side of the core layer that prevents the absorbed body fluids from leaking outside. Moreover, in general, in absorbent articles such as disposable diapers like paper diapers or sanitary napkins and the like, in addition to the back sheet, water repellent side sheets are provided at both sides of the absorbent articles so as to prevent absorbed liquid such as body fluids from leaking when the absorbent articles are displaced from the desired place due to the user's physical motion or when a user lays down on his/her side. (In the case of disposable diapers, since the water repellent side sheets often are provided with gathers, they are called a side gather or a leg cuff etc. In the case of disposable diapers, such side sheets are provided in a place that holds the joints of the thigh or the circumference of the thigh.) In addition, in the disposable diapers, a water-repellent round sheet comprising a non-woven fabric or the like also is provided at the skin side of the portion covering the abdomen or the portion covering the upper buttock located opposite to the abdomen, in order to prevent the liquids such as body fluids or the like, which are absorbed by the absorbent articles and which leak to the abdomen portion or the upper buttock portion, from leaking outside of the absorbent articles when the user falls down or lays down or turns the body. Moreover, in the disposable diapers, a belt-like waist gather etc. often is provided in the waist portion. Such gathers also comprise a water repellent sheet comprising a non-woven fabric or the like.
Moreover, for the core layer, various kinds of appropriate absorptive core layers are used. Such absorptive core layers comprise the compressed mixture in which an aggregate of fibers comprising cellulose type fiber such as fluff pulp etc., with which if necessary further synthetic fibers mixed, and a high water absorptive resin are mixed and compressed to harden. This absorptive core layer is, in general, wrapped up by, for example, tissue paper. Moreover, as a back sheet, a thermoplastic film is usually used. The thermoplastic film has a large number of minute micropores so as to prevent stuffiness inside when worn and to provide ventilation. Moreover, from the view point of improving the plastic-like touch and appearance peculiar to films, or from the viewpoint of improving the strength, the composite comprising a film and a non-woven fabric also is used. In addition, in order to provide various kinds of functions, there are absorbent articles comprising additional layers to which the other sheets are inserted further. Necessary portions between these sheets are adhered by using appropriate hot melt type adhesives or by means of thermal compression bonding.
However, the hot melt type adhesives have stickiness, so that the adhesive strength is no more strong than the case of adhesion with the pressure sensitive adhesives is. Furthermore, if too much hot melt type adhesives is used, clogging in each sheet occurs, thus damaging the ventilation or deteriorating permeability with respect to body fluid. Moreover, in a case where the conventional filament non-woven fabric comprising a single component is used for each member of these absorbent articles and bonded by thermal compression bonding, the adhesive strength is insufficient or the bonded portion tends to be ruptured because of the damage by thermal compression.
Olefin binary copolymer or olefin terpolymer such as ethylene-propylene random copolymer or ethylene-butene-propylene random copolymer used as a thermal adhesive component of the non-woven fabric comprising thermal adhesive conjugated filaments shows a relatively low tacticity, a low crystallization property, low melting point or low softening point properties by introducing ethylene or ethylene and butene into the polypropylene molecular chain. Moreover, the frictional resistance between fibers or between fiber and metal is relatively high, although they differ depending on the additive ratio of ethylene or ethylene and butene.
Therefore, there are some problems: when fibers discharged from the spinning nozzle holes are drawn by the metallic air sucker, the non-uniformity of fineness occurs due to the friction between metals or between fibers; or the fibers form bundles and are not easily opened.
Moreover, in a case where the resin having low crystallinity is used like the above, the time or distance (solidification length) in which resin fiber discharged from the spinning nozzle holes in a melting state is crystallized and solidified becomes remarkably long.
Therefore, in such non-woven fabrics, filaments form bundles due to the friction and non-uniformity of fineness or poor opening occurs, and furthermore the distance between filaments is short. As a result, filaments whose solidification length becomes long contact with each other in a molten state, namely, in a state where a low melting point or a low softening point olefin copolymer is melting, thus causing so called filament breakage and deteriorating the operating efficiency.
JP-A 5-5261 discloses the non-woven fabric made of conjugated filaments comprising ethylene-propylene random copolymer and isotactic polypropylene. In this disclosure, however, no way to avoid the above mentioned problems is particularly described.
Moreover, JP-A 5-263350 discloses a filament non-woven fabric in which the softness is enhanced by using ethylene-propylene random copolymer alone, and the above mentioned non-uniformity of fineness, poor opening, and the operating inefficiency due to the filament breakage are improved by adding nucleating agents. Therefore, it is thought that if the above mentioned two techniques are combined, even a conjugated filament in which one part of olefin binary copolymer or terpolymer such as ethylene-propylene random copolymer or ethylene-butene-propylene random copolymer is exposed to the surface of the filament can easily provide a non-woven fabric which is excellent in the uniformity.
However, in the technique disclosed in JP-A 5-263350, 3-methyl-1-butene copolymer that is a resin exhibiting a strong nucleating effect is used as the nucleating agent of ethylene-propylene random copolymer.
Consequently, the use of this nucleating agent results not only in an increase in crystallization initiation temperature but also enhances the orientation crystallization of ethylene-propylene random copolymer having an increased tension in melting state at the time of high speed spinning that is peculiar to the spun bond method. The resultant filaments have a much higher melting point or softening point than that of ethylene-propylene random copolymer resin itself. Moreover, the filaments having the fine fineness cannot be obtained easily due to the increase of the melt tension. Furthermore, in a case where the filaments having fine fineness are spun in this state, a tension greater than the breaking strength of melting filaments is developed, thus causing filament breakage.
In other words, in the technique disclosed in the above mentioned Laid Open Patent, the characteristics such as softness, excellent adhesiveness or low temperature adhesive property or the like of the low melting point or low softening point olefin copolymer such as ethylene-propylene random copolymer or ethylene-butene-propylene random copolymer cannot be fully brought out, and therefore the resultant filament non-woven fabrics are not sufficient in the hand feeling such as softness or touch etc.
The object of the present invention is to avoid the above mentioned problems and to provide a filament non-woven fabric comprising conjugated filaments having a high adhesive property, an excellent low temperature adhesive property, providing the resultant filament non-woven fabric with an excellent hand feeling such as softness or touch etc, and uniformity of the non-woven fabric, and having a high operating efficiency such as spinning property.
Another object of the present invention is to avoid the above mentioned problems of the conventional absorbent articles and by using the above mentioned filament non-woven fabric in at least one portion of the absorbent article to provide an absorbent article which has an excellent hand feeling such as softness or touch etc. and which is well adhered to the other members so that layers constituting the absorbent articles are not peeled apart or do not lose their shape at the time of using.
The present inventors intensively investigated and found that if inorganic powder is added at least to the first component, namely, a low melting point component or low softening point component, and the inorganic powder is exposed to the surface of fibers, minute unevenness is provided on the surface of fibers and the area where the fibers contact with each other is reduced, and adhesion between the fibers during spinning can be inhibited, so that filament breakage is decreased to make the operating efficiency good. It also was found that when inorganic powder is added, the crystallization temperature of olefin copolymer hardly increases and the increase in the crystallization is remarkably small, and therefore a filament non-woven fabric which is excellent in hand feeling such as softness or touch etc. can be obtained without damaging the properties of low melting point or low softening point olefin copolymer, for example, softness, excellent adhesion properties, low temperature adhesion properties or the like. It also was found that when such filament non-woven fabric is used for at least one portion of the absorbent article, the absorbent article is excellent in hand feeling such as softness or touch etc., with good adhesion between the other members so that the layers of absorbent articles are not peeled apart from other layer are not broken, thereby reaching the present invention.